Zirconium bearings and process of producing same



June 6, 1961 R. D. WATSON 7 2,987,352

ZIRCONIUM BEARINGS AND PROCESS OF PRODUCING SAME Filed Feb. 10, 1958 ATTORNEY United States Patent ()7 2,987,352 ZIRCONIUM BEARINGS AND PROCESS OF PRODUCING SAME Robert D. Watson, Chalk River, Ontario, Canada, as-

signor to Atomic Energy of Canada Limited, Ottawa, Ontario, Canada Filed Feb. 10, 1958, Ser. No. 714,133 3 Claims. (Cl. 308241) This invention relates to zirconium bearing members and to a process of producing them.

The problem of providing a bearing which will satisfactorily meet unusual service conditions such as lack or absence of lubrication or use of abnormal lubricants such as water and steam, has heretofore been recognized.

An object of the present invention is to provide a hearing member which will resist corrosion, galling, and wear under such unusual conditions, which will avoid'build up sistant bearing member. consisting essentially of a body of zirconium metal havington its surface a blue-black zirconium dioxide layer formed by oxidation of the surface portion of said body.

The invention will be described with reference to the accompanying drawing, in which- FIGURE 1 is a sectional elevation of a friction bearingstructure utilizing a'bearingin accordance withthe invention,

. iFIGURE'Z is a sectional elevation of a somewhat modified form of bearing structure, a a

FIGURE 3 is a sectional elevation of a further modified form of bearing structure, and

FIGURE 4 is a sectional elevation of a thrust and guide bearing structure also utilizing a bearing in accordance with the invention.

Referring to FIGURE 1, the bearing structure illustrated comprises a tubular bearing 1 which constitutes the bearing member in accordance with the invention and in which is journalled a shaft 2, the latter being provided with a journal insert 3 for engagement with the bearing.

The bearing 1 consists of a body 4 of zirconium metal which has been formed in the desired shape and subjected to an oxidizing atmosphere to form on its surface a zirconium dioxide layer 5.

Referring to FIGURE 2, the bearing member of the present invention is in this instance a journal insert 6 on shaft 2, the bearing proper being indicated at 7. The journal 6 consists of a body 8 of zirconium metal having a zirconium dioxide layer 9 formed on its surface.

' Referring to FIGURE 3, each of the journal insert 10 and bearing 11 is a bearing member in accordance with the invention. Journal 10 consists of a body 12 of zirconium metal having a zirconium dioxide layer 13 formed 2,987,352 Patented June 6, 1961 ice on its surface. .Bearing 11 consists of a body 14 of zirconium metal having a zirconium dioxide layer 15 formed on its surface.

Referring to FIGURE 4, the shaft 16 is provided with a guide bearing 17 and complementary journal insert 18, as well as a thrust bearing collar 19 and complementary thrust washer 20 carried by the shaft as by a nut 21. Guide bearing 17 consists of a zirconium metal body 22 having a zirconium dioxide layer 23 on its surface. Thrust bearing 19 consists of a zirconium metal body 24 having a zirconium'dioxide layer 25 on its surface.

Each of the bearing elements, in accordance with the invention, such as illustrated at 1, 6, 10, 11, 17 and 19, is produced by first forming the element from a body of zirconium metal, which is preferably hafnium free, in the shape of the required bearing member.

The shaped body is now subjected to oxidizing conditions whereby the surface metal oxidizes to form a layer ,of zirconium dioxide on the main body of metal. It is quite important that the oxidizing step be conducted only to a point where the zirconium dioxide formed is of particular crystalline form. Zirconium dioxide occurs in vari- 'ous crystalline modifications, including monoclinic tetragor'ral, cubic and hexagonal. For the purpose of the present invention, it is, of course, essential that the oxide layer be firmly adherent to the main body of metal. It has been found that if the oxidation of the surface of the zirconium body is conducted to the point where a zirconium dioxide of distinctive black or blue-black color is produced, the resulting oxide layer will be tenaciously adherent to the main body. This oxide layer is of highly oriented monoclinic crystalline form. On the other hand, if, for instance, the oxidation were continued until a white dioxide layer of normal monoclinic crystalline structure were produced, such layer would tend to separate and break ofi. The zirconium dioxide layer of the present invention is, as indicated above, a distinctive blackor blue-blackin color and has a density of approximately '5 .31 grams/ cubic centimeter. v

7 The oxidation step is conducted'in any suitable manner. -Thus','itmay'.be efiec'ted' by heating the zirconium body in air, oxygen, steam or hot water. A convenient manner of conducting the step is simply to place the bodies in an electric furnace and heat the same in an atmosphere of air. The bodies may thereby be oxidized at temperatures ranging from 700 C. to 900 C. for periods ranging from /2 hour to six hours or more. At the higher temperatures, oxidation takes place quite rapidly and care must be taken to regulate the time of treatment since too long an oxidation period will produce an excessive dimensional change and a white oxide formation of normal monoclinic crystalline structure. If a large number of bearing members are treated at one time, it may be desirable to feed air into the furnace. The rate of air feed may be approximately one cubic foot per hour per hundred square inches of surface area of the bearing members under treatment. It is desirable that a thick blueblack oxide layer be produced with a minimum of dimensional change. A temperature of 800 C. and a period of two hours is generally effective in producing these desirable results. The oxide coating produced has a thickness of from approximately 0.0002" to 0.0015" and the resulting bearing element has an increase in diameter of approximately 0.0015" per inch of diameter of the element.

The bearing element so produced with a surface consisting of a tightly adherent corrosion product has good corrosion, galling and wear resistance when employed under unusual service conditions. For instance, the element is quite satisfactory for use as a bearing with water lubrication only.

The following table gives the results of Wear tests which been conducted using a bearing 0.939" OD. x 0.750" ID. by long, and a journal 0.750" x long, completely immersed in water, thejournal rotating at a speed of .56 'fee't'per second and thebearing held stationary.

5 body and having a density of 5.31 grams per cubic centimeter and a thickness ranging from 0.0002 inch to 0.0015 inch.

3. A bearing member consisting essentially of a body of zirconium metal having a tightly adherent surface layer of zirconium dioxide formed by oxidation of the surface portion of said body, said layer having a distinctive blueblack color and a thickness ranging from 0.002 inch to 0.0015 inch.

Material Load, Weight Loss in p.s .i. of Milligrams Millions Pro ected of Revo- Area lutions Journal Bearing Journal Bearing 416, Stainless steel of Hai'nium free zirco- 27 433 8.7

Rockwell C45 hardnium with oxide ness. layer described. 416 Stainless steel of Hafnium free zirco- 27 240 4.8 6.2

Rockwell C45l1ardnium with oxide ness. layer described. Hard chrome plated afin'um 'free zirco- 34 3 2.5

304 stainless steel. mom with oxide layer described.

304L Stainless steel Zirconium with sur- 38 90 14 8.2

with a surface oxide face oxide layer delayer produced by scribed.

heating inair at 900 O. for two hours. SOtStainless steel Waukesha8 8alloy. 34 255: 285 1.86

The corrosion rate of the bearing elements described at moderate temperatures is low and no appreciable buildup of corrosion products occurs during periods of inoperation. The wear and galling resistance is high, as previously indicated. It is believed that the oxide layer is partially renewed by the heat generated-in the rubbing action of the surface under light loads. The hafniumfree zirconium has a low neutron capture cross-section which permits its use as a bearing material in high flux regions ofa reactor.

The bearing element described operates satisfactorily with water lubrication only in contact with various materials including hard chrome plate, Waukesha 88 alloy, 416 stainless steel both hardened and unhardened, chromallized 304 stainless steel, chromallized 1020 steel and 304 stainless steel.

I claim:

1. A'bearing member consisting essentially of a .body of zirconium metal having a tightly adherent surface layer of blue-black zirconium'dioxide of monoclinic crystalline form, formed by oxidation of the surface portion of said body.

References Cited in the file of this patent UNITED STATES PATENTS A Comprehensive Treatise on Inorganic and Theoretical Chemistry by J. W. Mellor, Langmon, Green & 00., New York, N.Y., 1927, vol. VII, pages 123-128 relied on.

Some Properties of High Purity Zirconium and Dilute Alloys With Oxygen by R. M. Treco, published by American Society for Metals, Cleveland, Ohio, 1952, 19 pages, pages 6, "7 and 12 relied on.

The Properties of Zirconium 'by 'F. W. 'Boulger- .E.c.D. 2726, Technical information Division, 'A.E.C;,

Oak Ridge, -Tenn., March 15, 1949, 82-page s, pages 19, 21 and 29 relied on. 7 

1. A BEARING MEMBER CONSISTING ESSENTIALLY OF A BODY OF ZIRCONIUM METAL HAVING A TIGHTLY ADHERENT SURFACE LAYER OF BLUE-BLACK ZIRCONIUM DIOXIDE OF MONOCLINIC CRYSTALLINE FORM, FORMED BY OXIDATION OF THE SURFACE PORTION OF SAID BODY. 